(1) Field of the Invention
This invention relates to the art of die casting using various hot metals such as zinc alloys, aluminum, lead, tin, brass, and magnesium. More specifically, the instant invention relates to a die casting apparatus for pumping molten metal from a heated container to an injection nozzle communicating with an inlet of a mold.
(2) Description of the Prior Art
The prior art apparatus typically includes a conventional electric crucible furnace for melting and holding casting metal and a pumping assembly for pumping the metal from the crucible to the injection nozzle. In one popular arrangement known as the "hot chamber" method, the pumping assembly includes a shot barrel and gooseneck assembly which is physically immersed in the crucible of the furnace and is selectively operated to pump the hot metal to the injection nozzle. These "hot chamber" machines are capable of high volume production of high quality die cast parts. However, they are unsuitable for casting high melting point metals such as aluminum since the aluminum attacks the ferrous material of the pumping assembly. When casting high melting point metals such as aluminum, a "cold chamber" arrangement has typically been employed in which molten metal from a remote melting pot is ladled into an opening in the upper wall of a horizontal shot cylinder and forced into the die by a plunger. These "cold chamber" machines substantially prevent the molten aluminum from attacking the ferrous material of the pumping assembly. However, these machines do not readily lend themselves to high volume production and, due to the extremely high pressures generated, require very substantial and very expensive construction. Attempts have been made to adapt the "hot chamber" machine to die casting of high melting point metals by providing a ceramic lining in the gooseneck passage. However, this arrangement has not been widely adapted since the lining is difficult to initially manufacture and difficult to replace after the inevitable wear has occured.